1. Field of the Invention
The present invention relates to a semiconductor module, and in particular it relates to a non-insulated power semiconductor module.
2. Description of the Related Art
Lately, semiconductor modules are being widely used not only to process control signals, but also to control large electric currents. For example, a power semiconductor module with a large current capacity is used in a control device for driving the motor for running an electromotive vehicle, such as a battery-powered forklift, etc., as a switching device installed between a battery and the motor.
For such semiconductor modules, semiconductor modules with a variety of structures, such as, a semiconductor in which the current capacity is enlarged by connecting power semiconductor chips of the same kind in parallel, a semiconductor module which is constituted as a simple circuit with several kinds of semiconductor chips, a semiconductor module which has an embedded driving circuit composed of semiconductor chips, etc., are known.
A semiconductor module, in particular a power semiconductor module, is usually formed by building one of the semiconductor chips described above in a resin package. The package is usually made of plastics, and the semiconductor chip is insulated using ceramics, etc. The space inside the package is filled up with gel, epoxy resin, etc.
A power semiconductor module generates a large amount of heat, since a large current flows through the module. Therefore, measures must be taken to radiate the heat. A method for installing a semiconductor module on a base substrate which has both a large heat capacity and a high heat radiation effect is often used to radiate the heat of semiconductor modules. In this case, the heat generated by a semiconductor module is radiated through the base substrate.
FIG. 1A shows the internal structure of a conventional semiconductor module. A MOSFET is used as an example here.
A semiconductor module 100 includes a plurality of semiconductor chips 101 which are connected to each other in parallel (three semiconductor modules 101a, 101b and 101c in FIG. 1A). A plurality of semiconductor chips 101 are arranged in a straight line with the respective drain region connected to the conductive base substrate 102. Semiconductors with such a structure are often termed xe2x80x9cnon-insulatedxe2x80x9d.
A source electrode 103 and a gate electrode 104 are formed in parallel with the arranging direction of the plurality of semiconductor chips 101. The source electrode 103 and gate electrode 104 are connected to a source region and a gate region, respectively, of each semiconductor chip 101 using bonding wires 105. The source electrode 103 and gate electrode 104 are electrically insulated from the base substrate 102 using an insulation sheet 106.
A drain terminal 107, a source terminal 108 and a gate terminal 109 are connected to the base substrate 102, source electrode 103 and gate electrode 104, respectively. The drain terminal 107 and source terminal 108 are an input point and an output point of the main current of this semiconductor module, respectively.
Each of the semiconductor chips 101 are turned on, when a control voltage is applied between the gate and source. In this case, the main current which is supplied through the drain terminal 103 reaches the source terminal 108 through the base substrate 102, each of the semiconductor chips 101, bonding wires 105 and source electrode 103 in this order. Here, the base substrate 102 functions as a drain electrode.
However, as shown in FIG. 1A, in a conventional semiconductor module 100, only one drain terminal 107 and only one source terminal 108 are usually provided in either end of the module. For this reason, as shown in FIG. 1B, the lengths of the path through which the main current flows are different depending on the position of the respective semiconductor chip 101. In the example shown in FIG. 1B, a path Ic through the semiconductor chip 101c is substantially longer than a path Ia through the semiconductor chip 101a. Here, inductance in a current path is nearly proportional to the length of the path. Thus, in this example, the inductance of the path Ic becomes larger than the inductance of the path Ia.
The influence of this inductance occurs at the time the semiconductor chip 101 is switched (especially, at the time the MOSFET is turned off). Specifically, the larger the inductance is, the larger the surge voltage that is generated at the time the semiconductor chip 101 is turned off is. Sometimes the semiconductor chip 101 is damaged since this surge voltage is applied to the semiconductor chip 101.
In a case that the length of a current path is different in each semiconductor chip, all the semiconductor chips do not operate in the same way even if the characteristics of all the semiconductor chips are the same. As a result, some of the particular semiconductor chips are easily damaged.
An object of the present invention is to suppress the surge voltage of a semiconductor module including a plurality of semiconductor elements.
In a semiconductor module of the present invention, a plurality of semiconductor chips are arranged in a straight line on a conductive substrate which functions as an electrode for inputting the main current. This semiconductor module comprises a terminal for inputting the main current, which is connected to the conductive substrate and is formed in parallel with the arranging direction of the plurality of semiconductor chips, and a terminal which is connected to the respective region for outputting the main current of the plurality of semiconductor chips and is formed in parallel with the arranging direction of the plurality of semiconductor chips. The end portion of at least one of the terminal for inputting the main current and terminal for outputting the main current is divided in parallel in the flowing direction of the main current.
If the terminal for inputting the main current is divided into two or more parts, the main current supplied to the respective semiconductor chip is to be inputted through the nearest divided part. If the terminal for outputting the main current is divided into two or more parts, the main current which flows through the respective semiconductor chip is to be outputted to the nearest divided part. In addition, the terminal for inputting the main current and terminal for outputting the main current are formed in parallel with the arranging direction of the plurality of semiconductor chips, respectively. Therefore, the main current of the respective semiconductor chip flows through the shortest path, and the lengths of all the paths are almost the same each other. As a result, the wiring inductances of all the semiconductor chips become uniform and small, and thus the surge voltages which are applied to the semiconductor chips also become uniform and small.